Actually -- it's so close to perfect I almost missed a quick flaw. When I do this, the first grouping of '1's only count up to 19 for some reason -- which throws off the rest (that correctly count to 20).

Any idea why? I'm using the formula in Cell M2 and the formula exactly how you wrote it above. If I change ROW(A1) to ROW(A2) for example, I've noticed that the first grouping of '1's go down to a count of 18 -- if you change it to ROW(A3), it goes down to a count of 17, etc. But the remainder of the list stays correct (all other numbers are groupings of 20).

Know what I can do about this? It's throwing everything off by one.